1. Field of the Invention
The present invention relates to a flip flop circuit and an apparatus using a flip flop circuit, and more particularly, to a double data rate (DDR) type flip flop circuit having a scan function and an apparatus using a DDR type flip flop circuit having a scan function.
2. Description of the Related Art
In recent years, in an LSI, there has been a demand for low power consumption and high speed operation. If a frequency of a clock signal is increased, power consumption of a circuit increases concurrently. Therefore, it is necessary to provide a flip flop capable of input and output data at a rate which is faster than the frequency of the clock signal.
As such a flip flop, there is known a DDR type flip flop for latching and outputting data at a speed which is two times as fast as the frequency of the clock signal. As the DDR type flip flop, there is known a circuit which includes two latch circuits and one selector (for example, refer to U.S. Pat. No. 6,525,565).
However, the flip flop of the U.S. Pat. No. 6,525,565 fails to comprise a scan function for inputting and outputting scan data used for testing. In general, in an LSI, it is necessary to use a flip flop with a scan function in order to achieve an operating test of an internal circuit. Therefore, it is necessary to achieve such a DDR type flip flop with a scan function. However, if a scan circuit for executing a scan function is added to the DDR type flip flop without changing a configuration, the number of elements required for the configuration of the DDR type flip flop is significantly increased.